In recent years, due to improvements in camera technology, use of monitoring systems in which monitoring cameras are used has increased. With these monitoring systems, an intrusion detection area is set in an image acquired from the monitoring camera, and a warning is output to a manager if an intender intruding in the intrusion detection area is detected (e.g., see Patent Document 1).
Also, although the monitoring system normally detects an intruder by extracting changes in an image, the larger the region to be extracted is, the greater the system load is, and the more time-consuming detection processing is. For this reason, a technique has been proposed in which a monitoring line called a “trip wire” is set in the image and a person who crosses the monitoring line is detected as an intruder (e.g., see Patent Documents 2 and 3).
Specifically, the monitoring system disclosed in Patent Document 2 detects an intruder by specifying a change region in which a feature amount changes in the image acquired from the monitoring camera and detecting interference between the specified change region and the monitoring line. Also, the monitoring system disclosed in Patent Document 3 detects an intruder by extracting pixels existing at the position of the monitoring line from an image acquired from the monitoring camera, arranging the pixels in a line to create a pixel data line, and then analyzing change in a time series in the pixel values of the pixel data line.